Mayo Clinic study is in preprint, not peer reviewed yet
New data on coronavirus vaccine effectiveness may be "a wakeup call"
A new preprint study that raises concerns about the mRNA vaccines' effectiveness against Delta — particularly Pfizer's — has already grabbed the attention of top Biden administration officials.
What they're saying: The study found the Pfizer vaccine was only 42% effective against infection in July, when the Delta variant was dominant. "If that's not a wakeup call, I don't know what is," a senior Biden official told Axios.
Driving the news: The study, conducted by nference and the Mayo Clinic, compared the effectiveness of the Pfizer and Moderna vaccines in the Mayo Clinic Health System over time from January to July.
Overall, it found that the Moderna vaccine was 86% effective against infection over the study period, and Pfizer's was 76%. Moderna's vaccine was 92% effective against hospitalization and Pfizer's was 85%.
But the vaccines' effectiveness against infection dropped sharply in July, when the Delta variant's prevalence in Minnesota had risen to over 70%
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Moderna was 76% effective against infection, and Pfizer was only 42% effective.
The study found similar results in other states.
For example, in Florida, the risk of infection in July for people fully vaccinated with Moderna was about 60% lower than for people fully vaccinated with Pfizer.
Between the lines: The two shots both use mRNA, but there are significant differences between them.
For example, Moderna is given in a stronger dose than Pfizer, and there is a slightly different time interval between shots.
"There are a few differences between what are known to be similar vaccines .... None of these variables is an obvious smoking gun, although the dosing amount seems the most likely to be a factor," Moore said.
article:
New data on coronavirus vaccine effectiveness against Delta raises concern among Biden administration - Axios
actual study
Comparison of two highly-effective mRNA vaccines for COVID-19 during periods of Alpha and Delta variant prevalence | medRxiv